You can message and share files inside your intranet without a server.
A New Kind of Instant Messaging
A universal instant messaging (IM) program
Development toolkit for Web Services and XML data bindings for C & C++
Chat Messenger. E-Mail-Client. Websearch. Filetransfer.
Open-source social network CMS and mobile apps.
MSN compatible messenger application
Secure chat and conferencing protocol
Network text chat (instant message) app requiring zero configuration
Underground IM is a free Java Instant Messaging solution.
Chat Messenger written in Java
A P2P Messenger which uses JXTA. It provides secure RSA/AES end-to-end